Bushing



June 17,1941. 4 f i FO D 2,2463% BUSHING Filed Feb. 23, 1939 WlTNES SES: INVENTOR %,Z/ amea 5; 5rd k?? a Patented June 17, 1941 UNITED STATES PATENT OFFICE BUSHING James G. Ford, Forest Hills, Pm, assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsyl- Vania Application February 23 1939, Serial No. 257,842 4 Claims. (Cl. 174-167) This invention relates generally to bushings, and in particular, to condenser bushings.

Where condenser bushings are constructed of layers of paper treated with a bond and layers of foil disposed in spaced relation therein, numerous difficulties are encountered. This is because the laminations of thewrapped bushing permit the transfer of oil and moisture through the bushing, with the result that the bushing is weakened mechanically, and where moisture is absorbed, the power factor of the bushing is increased, causing large dielectric losses, overheating and breakdown of the bushing.

Attempts have been made to overcome these difllculties even to the extent of impregnating the layers of paper with a material that is resistant to the effects of oil and moisture and which seals the laminations. Although the bushings thus constructed are resistant to the transfer of oil and the absorption of moisture rendering them substantially leak-proof, it is found that the advantages of moisture-proofness are oifset by an accompanying large increase in the power factor.

An object of this invention is to provide a bushing which is resistant to the transfer of moisture along and between its laminations.

Another object of this invention is to provide a bushing which is so sealed as to prevent the transfer of moisture along its laminations without detrimentally aifecting the power factor.

A more specific object of this invention is to provide a sealed condenser bushing formed from a plurality of layers of dielectric material having condenser plates disposed in spaced relation therein, in which the seal is effected by applying an oil capable of being oxidized and polymerized to the laminations adjacent the edges only whereby the ends are sealed without detrimentally affecting the power factor of the bushing.

Other objects of this invention will be apparent from the following description when taken in conjunction with the accompanying drawing, in which:

Figure 1 is a view in elevation of apparatus suitable for making the bushings of this invention;

Fig. 2 illustrates diagrammatically the apparatus showninFig. 1;

Fig. 3 illustrates diagrammatically apparatus for producing an embodiment of this invention; and

Fig. 4 illustrates a view in section of a bushing constructed in accordance with this invention.

This invention is an improved bushing of the I determined speed by insulator type or of the condenser type, and is particularly efi'ective as embodied in condenser bushings. By way of example, this invention is illustrated in Fig. 4 of the drawing as embodied in a condenser bushing l0. As a general rule, the condenser bushing I0 is formed of alternate concentric layers of condenser plates l2 and solid dielectric material It disposed about a supporting stud I5 which may also be a conductor. The dielectric material ll between and covering the condenser plates [2 is formed of a plurality of layers l8 of fibrous material, such as paper, in sheet form with at least one of its surfaces treated with a suitable binder, such as shellac, which under predetermined conditions will bond the layers together when the bushing is wrapped.

In making the bushing l0, winding apparatus l9 of the type illustrated in Figs. 1 and 2 or in Fig. 3, is employed. This winding equipment comprises a heated plate 20 and a plurality of pressure rolls 22, 24 and 26 disposed in spaced relation to each other and adjustably mounted for applying pressure to the bushing 10 positioned between the rolls as it is being formed. The supporting stud I6 may be rotated at a preany suitable driving mechanism, not shown, which for driving the rolls 22, 24 and 26. As illustrated in Fig. 1, a plurality of oil cups 28 are provided and disposed to be slidably mounted on a supporting rod 36 for positioning them as the operator of the equipment desires. The positioning of the oil cups 28 may be automatically controlled with respect to the size of the bushing which is being formed, or may be manually controlled, as will be explained more fully hereinafter.

In forming the bushing, the fibrous material in sheet form is drawn from a roll 32 and passed over the heated plate 20 to the supporting stud l6 where the rolls 22, 24 and 26 eflectively compress the layers l8 of the fibrous material on the supporting stud. In order to provide for bonding the laminations into a unitary structure, the fibrous material is usually treated with a binder which softens under the action of heat. Shellac is satisfactory for this purpose and is usually provided on one of the surfaces 01' the sheet of fibrous material. As the sheet or fibrous material is drawn from the roll 32 over the heated plate 20, the shellac is so softened that as the sheet is wound upon the supporting stud IS, the shellac eifectively bonds or cements the adjoining layers of the bushing.

Since it has been found that the laminations may also be employed bonded together with shellac are not resistant to the transfer of oil and moisture, it is necessary to provide for sealing the ends of the bushing. In order to accomplish this result, tung oil or oiticica oil, each of which is capable of being oxidized and polymerized is applied to the bushing in a manner which will not detrimentally afrect the power factor of the finished bushing. This is accomplished by permitting the oil to drip from the oil cups 28, which have suitable openings therein, at a predetermined rate of flow onto the sheet of fibrous material, as shown in Fig. 2, just prior to the passing of the paper onto the supporting stud between the pressure rolls.

In practice, the oil is so dripped from the cups 28 which are positioned with respect to the sheet of fibrous material being wound, that the oil is,

applied to only a band of the fibrous material adjacent the edges only of the finished bushing.

/ Thus, if in winding the bushing, it is desired to terial on the stud where it forms a small bead 84 between the pressure roll 22 and the bushing and is rolled in a narrow band into the uncoated side of the fibrous material on the stud under pressure. Usually the rolls 22 and 24 are heated in order to aid in the impregnation of the fibrous material and the bonding of the shellac coated layers to the adjoining layer of the wound bushing. In practice it is found that the heat applied is also sufiicient to partially solidify the oil in the narrow band. Baking the wound bushing at temperatures of 100 C. to 125 C.- cures the oil to effectively seal the bushing.

In making condenser bushings, a predetermined number of layers of fibrous material are wound upon the supporting stud l6 after which the sheet of fibrous material is cut and a condenser plate |2 of metal foil or other suitable material is wrapped around the previously wound layers of fibrous material. Usually the condenser plate is coated on its external surface with shellac to aid in the continued wrapping of the bushing, whereby the sheet of fibrous material is bondedto the condenser plate upon the continuation of the winding of the fibrous material. The winding of the fibrous sheet material is interrupted as many times as is necessary in winding a condenser bushing of any predetermined size having any predetermined number of condenser plates separated by layers of the solid dielectric material.

Where it is desired to wind a condenser bushing having tapered ends, it is usually not economical to employ sheets of fibrous material of difierent size. Instead, the entire bushing is wound from the same size of sheet of fibrous material, the winding being interrupted only to introduce the condenser plates l 2 in predetermined relation in the fibrou material. By manually adjusting the position of the oil cups 28 as the bushing is wound, the oil. is applied to only a narrow band along which the wound bushing is later machined to form the tapered end. This narrow band is usually defined by so controlling the flow of oil to limit it to extend inwardly along the laminations not more than one inch beyond the edge of the condenser plates and usually one inch outside of the edge of the condenser plates. The excessive fibrous material at the end of the bushing can readily be machined from the wound bushing, leaving a solid tapered end sealed with the 011.

As applied with the apparatus of Fig. 2 of the drawing, the oil is delivered to the shellac coated surface of the fibrous material and in order to secure better impregnation of the fibrous material, apparatus as shown in Fig. 3 may be employed. In this form, the sheet of fibrous material is pressed through an auxiliary set of pressure rolls 36 and 38 prior to passing the fibrous material over the heated plate 20. The oil cups 28 are so disposed between the roll 32 of fibrous material and the auxiliary pressure rolls 36, 38 that the oil which is capable of being oxidized and polymerized is delivered in a narrow band to the untreated surface of the sheet of fibrous material and is rolled into the fibrous material by the auxiliary rolls 36 and 38. The fibrous material carrying the narrow band of rolled-in oil is then passed over the heated plate 20 to the supporting stud l6, the action of the heat from the plate 20 and the pressure rolls 22 and 24 aiding in effectively sealing the bushing as it is wound between the pressure rolls 22, 2 5 and 26. Other steps of winding the bushing with this equipment are the same as those described hereinbefore with respect to the winding of a bushing with the equipment of Figs, 1 and 2.

By winding the bushing by rolling in the oil in the liquid state in a narrow band at the ends only of the bushing and solidifying it under the action of the heat, it is found that bushings are produced which have better impulse values, better radio interference values and a better power factor, leading to better BO-cycle hold breakdown values. Further, there is no loss of the oil and since it is applied in a narrow band adjacent only the edges of the fibrous material, there is less chance of the oil interfering with the adhesion of the fibrous material with the condenser plates.

Although this invention has been described with reference to embodiments thereof, it is, of course, not to be limited thereto except insofar as is necessitated by the prior art and the scope of the appended claims.

I claim as my invention:

1. A bushing comprising a supporting stud, a solid dielectric material in sheet form applied to the stud in layers, a binder applied to the layers to cement them into a unitary structure, a polymerized oil selected from the group consisting of tung oil and oiticica oil carried by the layers of dielectric, the oil being applied to and carried by only a band of predetermined width adjacent the edges of the layers to seal the ends of the bus-hing without detrimentally affecting its power factor.

- -2. A bushing comprising a supporting stud, a solid dielectric material in sheet form-applied to the stud in layers, a binder applied to the layers to cement them into a unitary structure, tung oil applied to the layers of dielectric, the tung oil being applied to only a band of predetermined width adjacent the edges of the layers to seal the ends of the bushing without de'trlmentally affecting its power factor.

3. A bushing comprising a supporting stud, dielectric material in sheet form applied to the stud in layers, and a polymerized tung oil carried by a band of predetermined width adjacent the 2,24a,3oo 3 edges only of the layers of dielectric material, the tung oil impregnating the dielectric material and sealing the ends of the bushing without detrimentally afiectlng its power factor.

4. A bushing comprising. a supporting stud, a dielectric material comprising fibrous material in I sheet i'orm having one of its surfaces coated with a binder applied to the stud in layers, and

JAMES G. FORD. 

